The Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards define a family of protocols for implementing Wireless Local Area Networks (WLAN). The communication range is up to a few hundred meters and usually is about two to three hundred meters. The standards is created and maintained by IEEE Local Area Network/Metropolitan Area Network (LAN/MAN) Standard Committee (IEEE 802). The standards are used in various scenarios such as networks for home/offices, factories, and cellular communications.
The IEEE 802.11 standard is designed as communication protocols for Wireless Local Area Networks (WLAN). Usually, an access point (AP) works with a few to a few tens of stations (STAs) associated to it and within a range of a few hundred meters. The current standard can easily handle such a small scale of networks.
However, with new application scenarios for WLAN, such as Smart Grids for power networks, an AP may required to extend its coverage to 1 km, and handle a few thousands of nodes (up to 6000 as required by the 801.11 ah standard amendment requirements) with low transmission speed. Several problems, including power savings for the stations may arise if the current 802.11 standard is used.
IEEE802.11-12/0114r0 notes that battery powered devices may limit power consumption by limiting the active/awake/receive time. Devices consume power when listening for beacons with traffic indication map (TIM) frames.
A device with a long doze period may be required to wake up early due to clock drift during the long doze period. Also, a beacon with a TIM frame may require several milliseconds to complete transmission. These may increase duration in which the station is active/awake.
IEEE802.11-12/0114r0 proposes using an immediate power save (PS)-Poll protocol to limit power consumption. FIG. 1A is a schematic 100a showing the immediate PS-Poll protocol of an access point (AP) 102a and a station (STA) 104a, in which buffered data (or buffered units) 106 for the station (STA) 104a is pending in the access point 102a. FIG. 1B is a schematic 100b showing the immediate PS-Poll protocol of an access point (AP) 102b and a station (STA) 104b, in which no buffered data (or buffered units) 106 for the station (STA) 104b is pending in the access point 102a. The STA 104a, 104b is in doze state 108a, 108b, 108c, 108d most of the time, during which the STA 104a, 104b may not check for beacon signals with TIM frames 110. The STA 104a, 104b may also not be synchronized with the Time Synchronization Function (TSF). The STA 104a, 104b may wake up at the desired time 112a, 112b and sends a PS-Poll 114a, 114b to the AP. At this juncture, the STA 112a, 112b may not yet know if there is buffered data (or buffered units (BU)) 106 pending for it at the AP 102a, 102b for the STA 112a, 112b as it does not check for beacon signals with TIM frames previously. If there is buffered data (or buffered units (BU)) 106 pending, the AP 102a may respond immediately by either transmitting the buffered data (or buffered units) 106 or by sending an acknowledgement (ACK) frame 116a indicating there is buffered data (or buffered units) 106 in the AP 102 for the STA 104a (BU=1). If there is no buffered data (or buffered units) 106 pending in the AP 102b for the STA 104b, there may be an ACK frame 116b setting BU to be 0. The STA 104b may go to sleep if there is no buffered data (or buffered units) 106 pending in the AP 102b for the STA 104b. 
However, allowing the STAs to send PS-Poll signals anytime after wakeup may make contention worse if a large number of STAs wake up at almost the same time to contend on channel access. The STAs may have to wait for completion of other transmissions due to competing PS-Polls from multiple STAs. Also, the overall transmission time spent to receive individual ACK frames for a large number of STAs may be long. Power consumption for awaiting STAs may be high due to low data rate even with the immediate PS-Poll mechanism. In addition, multiple STAs may have to send the PS-Poll signals within a relatively short period of time even only when a few STAs may need to receive buffered data from the AP. Furthermore, a target beacon transmission time (TBTT) may be just shortly after a STA sends the PS-Poll, which may result in unnecessary duplication.